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    <script>

        // 求两个数的和差积商  有参数，有返回值  (n1, n2, fuHao)   

        //    题目：判断符号

        function calc(a , b , fuHao)  {
            switch(fuHao) {
                case '+' : return a + b ;
                case '-' : return a - b ; 
                case '*' : return a * b ;
                case '/' : return a / b ;
            }
        }
        
        

    </script>

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